Brace Yourself for a Triple Wave of Seasonal Viruses

Every year it’s the same. As soon as it starts to get cold, people gather indoors. Windows are pulled shut. Commuters forgo walking or cycling, opting for packed buses and subways. Our whole world retreats to where it’s warm, our breath condensing on the windows of homes, offices, schools, and transport, showing just how well we’ve sealed ourselves off from the outside. We create, in short, the perfect breeding ground for viruses.

When the respiratory virus season begins, it’s usually quite predictable. Patients start being admitted to hospitals with influenza or respiratory syncytial virus (RSV) around October in the northern hemisphere. Thousands of people get sick, and many die, but the odd extreme year aside, health systems across Europe and North America aren’t typically at risk of being overwhelmed.

But the pandemic has derailed this predictability. It has added another virus to the seasonal mix, and flu and RSV are returning this year with a vengeance. A “twin” or even “tripledemic” could be on the way, with all three viruses hitting at once, illnesses soaring, and health systems creaking under the pressure. Already there are signs this is happening.

Many hospitals in the US are at capacitycaring for large numbers of children infected with RSV and other viruses, many more than would be expected at this time of year. The US Centers for Disease Control and Prevention (CDC) does not track RSV cases, hospitalizations, and deaths as it does for flu, but hospitals across the country have been reporting peak levels typically observed in December and January. Almost one in five PCR tests for RSV came back positive in the week ending October 29, with this rate having doubled over the course of a month. Generally speaking, the higher the proportion of tests that come back positive, the more common a virus is in the wider community. In the three years before the pandemic, an average of just 3 percent of tests came back positive in October.

This is a hangover from the pandemic. Over the past two years, RSV and flu were kept down thanks to the protective measures people took against the coronavirus: mask wearing, hand washing, and isolating. Between the beginning of the pandemic and March 2021, the weekly positivity rate for RSV tests remained below 1 percent, according to the CDC—down where it was in pre-pandemic times.

In July of this year, health specialists warned in The Lancet that the benefits of these pandemic precautions could end up having a negative effect this winter season. Reducing exposure to common endemic viruses such as RSV and flu, experts argued, risked creating an “immunity gap” in people either born during the pandemic or who had not previously built up sufficient immunity against these viruses.

That prediction now appears to be coming true, as children are catching these viruses for the first time, without having built up any prior immunity, and falling badly ill. “We’re seeing kids at older ages getting RSV that would have previously gotten it at a younger age,” says Rachel Baker, an assistant professor of epidemiology at Brown University in Rhode Island, who was a coauthor of the Lancet comment piece. “That’s putting some pressure on hospitals.”

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